Widespread adoption by major economies like the US.  Replacing the USD with Bitcoin is a radical notion, with significant economic and technological hurdles. The "unlimited supply" of USD as a weakness, but replacing it with a finite asset like Bitcoin presents its own challenges.  Imagine a society where the money supply is inflexible, potentially hindering economic growth.

Blackrock's purchase of Bitcoin is a case in point.  It represents a diversification strategy, not necessarily a mass adoption of Bitcoin as a transactional currency.  People do need oil, but widespread use of electric vehicles could disrupt the oil market.  Similarly, alternative cryptocurrencies like LTC or Doge could challenge Bitcoin's dominance for everyday transactions.